The effect of chronic ethanol consumption on temperature-dependent physical properties of liver mitochondrial membranes

Analysis of Mitochondrial Dimensions and Cristae Structure in Pluripotent Stem Cells Using Transmission Electron Microscopy

Dynamic alterations to mitochondrial structure and function regulate cell fate decisions and underlie multiple age-related and genetic diseases that are modeled using embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). Transmission electron microscopy (TEM) can be used to obtain high-resolution micrographs of mitochondria, but mitochondrial ultrastructure is easily distorted during specimen processing. This unit describes a method that preserves mitochondrial membrane structure from adherent ESC cultures for TEM sample preparation. This procedure is useful for assessing ultrastructural changes to mitochondria during differentiation, reprogramming, or experimental manipulation of ESC metabolism. We provide comprehensive protocols for: (1) preparation of ESC cultures for TEM; (2) retrieval of thin sections from individual ESCs; and (3) contrast staining and morphometric analysis of mitochondria and cristae. This unit also describes an alternative procedure for samples with low cell numbers and a supporting protocol for morphometric image analysis. Collectively, these protocols allow for the observation and quantitative analysis of mitochondria in ESCs. © 2018 by John Wiley & Sons, Inc.

Metabolism of ethanol and associated hepatotoxicity

Over the last three decades, direct hepatotoxic effects of ethanol were established, some of which were linked to redox changes produced by NADH generated via the alcohol dehydrogenase (ADH) pathway and shown to affect the metabolism of lipids, carbohydrates, proteins, and purines. It was also determined that ethanol can be oxidized by a microsomal ethanol oxidizing system (MEOS) involving a specific cytochrome P-450; this newly discovered ethanol-inducible cytochrome P-450 (P-450 IIEi) contributes to ethanol metabolism, tolerance, energy wastage (with associated weight loss), and the selective hepatic perivenular toxicity of various xenobiotics. Their activation by P-450IIEi now provides an understanding of the increased susceptibility of the heavy drinker to the toxicity of industrial solvents, anaesthetic agents, commonly prescribed drugs, over-the-counter analgesics, and chemical carcinogens. P-450 induction also explains depletion (and toxicity) of nutritional factors such as vitamin A. As a consequence, treatment with vitamin A and other nutritional factors is beneficial, but must take into account a narrowed therapeutic window in alcoholics who have increased needs for nutrients and also display an enhanced susceptibility to some of their adverse effects. Acetaldehyde (the metabolite produced from ethanol by either ADH or MEOS) impairs hepatic oxygen utilization and forms protein adducts, resulting in antibody production, enzyme inactivation, and decreased DNA repair. It also stimulates collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts, and causes glutathione depletion. Supplementation with S-adenosyl-L-methionine partly corrects the depletion and associated mitochondrial injury, whereas administration of polyunsaturated lecithin opposes the fibrosis. Thus, at the cellular level, the classic dichotomy between the nutritional and toxic effects of ethanol has now been bridged. The understanding of how the ensuing injury eventually results in irreversible scarring or cirrhosis may provide us with improved modalities for treatment and prevention.

Cytotoxicity of short-chain alcohols

Ethanol and other short-chain alcohols elicit a number of cellular responses that are potentially cytotoxic and, to some extent, independent of cell type. Aberrations in phospholipid and fatty acid metabolism, changes in the cellular redox state, disruptions of the energy state, and increased production of reactive oxygen metabolites have been implicated in cellular damage resulting from acute or chronic exposure to short-chain alcohols. Resulting disruptions of intracellular signaling cascades through interference with the synthesis of phosphatidic acid, decreases in phosphorylation potential and lipid peroxidation are mechanisms by which solvent alcohols can affect the rate of cell proliferation and, consequently, cell number. Nonoxidative metabolism of short-chain alcohols, including phospholipase D-mediated synthesis of alcohol phospholipids, and the synthesis of fatty acid alcohol esters are additional mechanisms by which alcohols can affect membrane structure and compromise cell function.

Studies on urea synthesis in the liver of rats treated chronically with ethanol using perfused livers, isolated hepatocytes, and mitochondria

Changes in urea synthesis in the liver of rats treated with 32% ethanol in the drinking water for up to 6 months were studied using perfused livers, isolated hepatocytes, and mitochondria. Results obtained from ethanol-treated rats are summarized as follows: (1) the mitochondria of the hepatocytes of rats treated with ethanol for 2 months or longer became enlarged to various degrees, (2) the levels of ammonia in the serum remained within a normal range, while those in liver tissue were elevated compared with the control, (3) urea synthesis from ammonia in perfused livers was decreased markedly, while that from citrulline remained in the normal range, (4) the activities of carbamyl phosphate synthetase (CPS; EC 2.7.2.5) and ornithine transcarbamylase (OTC; EC 2.1.3.3) in mitochondria were unchanged compared with those of the control, and (5) the levels of ATP in liver tissue and the ability of mitochondria to synthesize ATP were decreased markedly compared with the control. Both the level of ATP in the hepatocytes and the synthesis of urea from ammonia by perfused livers of rats treated with ethanol were resistant to externally added ethanol, while those of control animals were severely affected. These results suggest that the intracellular level of ATP is intimately related to urea synthesis in both control and ethanol-treated animals, and lowered levels of ATP may be a key factor in the suppression of urea synthesis in ethanol-treated animals.

The amino-terminal peptide of HIV-1 glycoprotein 41 interacts with human erythrocyte membranes: peptide conformation, orientation and aggregation

Structural studies assessed interactions between the amino-terminal peptide (FP-I; 23 residues 519-541) of the glycoprotein 41,000 (gp41) of Human Immunodeficiency Virus Type-1 (HIV-1) and human erythrocyte membranes and simulated membrane environments. Peptide binding was examined at sub-hemolytic (approx. less than 5 microM) and hemolytic (greater than or equal to 5 microM) doses (Mobley et al. (1992) Biochem. Biophys. Acta 1139, 251-256), using circular dichroism (CD) and Fourier-transform infrared (FTIR) measurements with FP-I, and electron spin resonance (ESR) studies employing FP-I spin-labeled at either the amino-terminal alanine (FP-II; residue 519) or methionine (FP-III; position 537). In the sub-lytic regime, FP-I binds to both erythrocyte lipids and dispersions of SDS with high alpha-helicity. Further, ESR spectra of FP-II labeled erythrocyte ghosts indicated peptide binding to both lipid and protein. In ghost lipids, FP-II was monomeric and exhibited low polarity and rapid, anisotropic motion about its long molecular axis (i.e., alpha-helical axis), with restricted motion away from this axis. The spin-label at the amino-terminal residue (Ala-519) is insensitive to the aqueous broadening agent chromium oxalate and buried within the hydrophobic core of the membrane; the angle that the alpha-helix (residues 519-536) makes to the normal of the bilayer plane is either 0 degree or 40 degrees. Contrarily, ESR spectra of ghost lipids labeled with sub-lytic doses of FP-III indicated high mobility and polarity for the reporter group (Met-537) at the aqueous-membrane interface, as well as extreme sensitivity to chromium oxalate. At lytic FP-I doses, CD and FTIR showed both alpha-helix and beta-structure for peptide in ghost lipids or detergent, while ESR spectra of high-loaded FP-II in ghost membranes indicated peptide aggregates. Membrane aggregates of FP-I may be involved in hemolysis, and models are suggested for N-terminal gp41 peptide participation in HIV-induced fusion and cytolysis.

Effects of adenosine administration on the function and membrane composition of liver mitochondria in carbon tetrachloride-induced cirrhosis

The effect of chronic carbon tetrachloride (CCl4) administration on liver mitochondria function and the protective action of adenosine on CCl4-induced damage were assessed in rats made cirrhotic by long-term exposure to the hepatotoxin (8 weeks). The CCl4 treatment decreased the ADP-stimulated oxygen consumption, respiratory control, and ADP/O values, mainly for substrates oxidation of site I, in isolated mitochondria. This impaired mitochondrial capacity for substrate oxidation and ATP synthesis was accompanied by an important diminution (approximately 30 mV) of membrane electrical potential. Disturbances of the mitochondrial membrane, induced by CCl4 treatment, were also evidenced as increased mitochondria swelling and altered oscillatory states of mitochondrial volume, both energy-linked processes. The deleterious effects of CCl4 on mitochondrial function were also reflected as a deficient activity of the malate-aspartate shuttle that correlated with abnormal distribution of cholesterol and phospholipids in membranes obtained from submitochondrial particles. Adenosine treatment of CCl4-poisoned rats partially prevented the alterations in mitochondria membrane composition and prevented, almost completely, the impairment of mitochondria function induced by CCl4. Although the nature of the protective action of adenosine on CCl4-induced mitochondria injury remains to be elucidated, such action at this level might play an important role in the partial prevention of liver damage induced by the CCl4.

Resistance to ethanol disordering of membranes from ethanol-fed rats is conferred by all phospholipid classes

Phospholipids extracted from liver microsomes and mitochondria of ethanol-fed rats retained the resistance to membrane disordered by ethanol which is observed in the intact isolated membranes. The lipid extracts were separated into the major phospholipid classes (phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol from microsomes and phosphatidylcholine, phosphatidylethanolamine and cardiolipin from mitochondria) by preparative TLC. The extent of membrane disordering by ethanol of phospholipid vesicles composed of a mixture of phospholipids from ethanol-fed rats and controls was determined from the reduction of the order parameter of the spin-probe 12-doxyl-stearate. In contrast to previous reports, we found that all phospholipid classes from ethanol-fed rats confer resistance to disordering by ethanol. To a first approximation the extent of resistance was proportional to the fraction of lipids from ethanol-fed rats, regardless of the phospholipid head-group. Subtle differences between phospholipid classes may exist but were too small to measure accurately. Except for phosphatidylethanol, incorporation of anionic phospholipids did not have a significant effect on the sensitivity of phospholipid vesicles to the disordering effect of ethanol. Vesicles prepared from mixtures of various dioleoyl phospholipids and natural phospholipids did not indicate a clear effect of fatty acid saturation on the sensitivity to disordering by ethanol. Although the precise molecular changes that occur in phospholipids from ethanol-fed rats have not been fully characterized it appears that subtle changes in all phospholipid classes contribute to the resistance to ethanol disordering of these membranes.

Alcohol, liver, and nutrition

Until two decades ago, dietary deficiencies were considered to be the major reason why alcoholics developed liver disease. As the overall nutrition of the population improved, more emphasis was placed on secondary malnutrition. Direct hepatotoxic effects of ethanol were also established, some of which were linked to redox changes produced by reduced nicotinamide adenine dinucleotide (NADH) generated via the alcohol dehydrogenase (ADH) pathway. It was also determined that ethanol can be oxidized by a microsomal ethanol oxidizing system (MEOS) involving cytochrome P-450: the newly discovered ethanol-inducible cytochrome P-450 (P-450IIE1) contributes to ethanol metabolism, tolerance, energy wastage (with associated weight loss), and the selective hepatic perivenular toxicity of various xenobiotics. P-450 induction also explains depletion (and enhanced toxicity) of nutritional factors such as vitamin A. Even at the early fatty-liver stage, alcoholics commonly have a very low hepatic concentration of vitamin A. Ethanol administration in animals was found to depress hepatic levels of vitamin A, even when administered with diets containing large amounts of the vitamin, reflecting, in part, accelerated microsomal degradation through newly discovered microsomal pathways of retinol metabolism, inducible by either ethanol or drug administration. The hepatic depletion of vitamin A was strikingly exacerbated when ethanol and other drugs were given together, mimicking a common clinical occurrence. Hepatic retinoid depletion was found to be associated with lysosomal lesions and decreased detoxification of chemical carcinogens. To alleviate these adverse effects, as well as to correct problems of night blindness and sexual inadequacies, the alcoholic patient should be provided with vitamin A supplementation. Such therapy, however, is complicated by the fact that in excessive amounts vitamin A is hepatotoxic, an effect exacerbated by long-term ethanol consumption. This results in striking morphologic and functional alterations of the mitochondria with leakage of mitochondrial enzymes, hepatic necrosis, and fibrosis. Thus, treatment with vitamin A and other nutritional factors (such as proteins) is beneficial but must take into account a narrowed therapeutic window in alcoholics who have increased needs for such nutrients, but also display an enhanced susceptibility to their adverse effects. Massive doses of choline also exerted some toxic effects and failed to prevent the development of alcoholic cirrhosis. Acetaldehyde (the metabolite produced from ethanol by either ADH or MEOS) impairs hepatic oxygen utilization and forms protein adducts, resulting in antibody production, enzyme inactivation, and decreased DNA repair. It also enhances pyridoxine and perhaps folate degradation and stimulates collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts.(ABSTRACT TRUNCATED AT 400 WORDS)

Chronic alcoholism impedes the recovery of renal function following renal ischemia

The recovery of renal function following renal ischemia was studied using rats fed for 1-, 3-, and 5-week periods with an alcoholic diet (ethanol provided 36% of total calories). Renal ischemia was produced by clamping the renal artery and vein for 20 min. Renal function was determined 24 hr after the ischemia. In the absence of ischemic insult, the renal function of rats fed with an alcoholic diet for 1, 3, and 5 weeks was not significantly different from those of nonalcoholic rats. In nonalcoholic rats, renal function (24 hr postischemia) were: glomerular filtration rate (GFR) 430.4 +/- 29.6 microliters/min/g KW (kidney weight), renal plasma flow rate (RPFR) 1.4 +/- 0.17 ml/min/g KW, and fractional sodium excretion (FENa) 2.0 +/- 0.04% (mean +/- SE). Postischemic renal function of rats on 1- and 3-week alcoholic diets were essentially the same as that of the control rats. However, the 24-hr postischemic renal function of 5-week alcoholic diet rats was significantly depressed. The values were only 117.2 +/- 35.2 microliters/min/g KW (p less than 0.05) for GFR, 0.31 +/- 0.12 ml/min/g KW (p less than 0.05) for RPFR, and 7.46 +/- 3.59% for FENa. The present results demonstrate that the rat kidney subjected to prolonged alcohol ingestion was more susceptible to renal insult than a nonalcoholic kidney.

Hepatic, metabolic and toxic effects of ethanol: 1991 update

Until two decades ago, dietary deficiencies were considered to be the only reason for alcoholics to develop liver disease. As the overall nutrition of the population improved, more emphasis was placed on secondary malnutrition and direct hepatotoxic effects of ethanol were established. Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins, and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) that contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens, and even nutritional factors such as vitamin A. In addition, ethanol depresses hepatic levels of vitamin A, even when administered with diets containing large amounts of the vitamin, reflecting, in part, accelerated microsomal degradation through newly discovered microsomal pathways of retinol metabolism, inducible by either ethanol or drug administration. The hepatic depletion of vitamin A is strikingly exacerbated when ethanol and other drugs were given together, mimicking a common clinical occurrence. Microsomal induction also results in increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of ethanol induced hepatic injury

Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) which contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Induction also results in energy wastage and increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen synthesis, thereby promoting fibrosis.

Cardiolipin from ethanol-fed rats confers tolerance to ethanol in liver mitochondrial membranes

In rats chronically consuming ethanol, the liver mitochondrial membranes develop resistance to the disordering effects of ethanol in vitro, so-called "membrane tolerance". To investigate the molecular basis of this tolerance in the inner mitochondrial membrane, multilamellar vesicles were produced by recombining the mitoplast phospholipids (quantitatively separated by preparative HPLC) from control and ethanol-fed animals in various combinations. The effect of in vitro ethanol on the physical properties of these vesicles was determined by electron spin resonance. Vesicles composed of all mitoplast phospholipids from control rats were disordered by 50-100 mM ethanol, whereas those made of the phospholipids from ethanol-fed animals were resistant. When phosphatidylcholine (46 mol %) or phosphatidylethanolamine (42 mol %) from ethanol-fed rats replaced the corresponding phospholipids of control rats, the vesicles were disordered by ethanol. By contrast, when as little as 2.5 mol % of cardiolipin (one-fourth the naturally occurring amount) from ethanol-fed rats replaced that phospholipid from control rats, vesicles were rendered entirely resistant to disordering by ethanol. The same amount of cardiolipin from ethanol-fed rats also conferred membrane tolerance to vesicles composed of bovine phospholipids, demonstrating that this effect is not restricted to rat mitoplast phospholipids. In vesicles composed of a single mitoplast-phospholipid class, only vesicles composed of cardiolipin from ethanol-fed rats resisted disordering. Phosphatidylinositol from liver microsomes of ethanol-fed rats also confers membrane tolerance and was the only microsomal phospholipid that formed tolerant vesicles. Thus, in livers of rats chronically fed ethanol, anionic phospholipids are selectively converted into potent promoters of membrane tolerance in both mitochondrial and microsomal membranes.

Liposomes as membrane model for study of lipid peroxidation

This article describes the properties, production and characterization of liposomes with special reference to their use as membrane model for the study of lipid peroxidation. It presents briefly the methods that can be used for the assay of liposomal lipid peroxidation and brings out the special advantages these liposomes provide in elucidating the mechanism of lipid peroxidation by different physical and chemical agents. Studies involving liposomal lipid peroxidation by different agents and the consequent changes in the structure and function of liposomal membrane have been reviewed briefly.

In vitro effects of ethanol on erythrocyte membrane fluidity of alcoholic patients: an electron spin resonance study

Chronic ethanol consumption has been shown to affect physical properties of membranes from animals as measured by electron spin resonance (ESR). This study compared for the first time the physical properties of erythrocyte membranes of alcoholic patients and control subjects using ESR procedures. Membrane fluidity was determined in the presence and absence of ethanol using the 5-doxyl stearic acid spin-label. Temperature-dependent phase transition also was determined, as were comparisons between ESR parameters, at the 1st and 5th week after alcohol withdrawal. Ethanol-induced fluidity was significantly greater in membranes of control subjects compared with alcoholic patients. Baseline fluidity did not differ and the temperature at which the phase transition occurred was not significantly different between the two groups. The resistance of membranes of alcoholic patients to fluidization by ethanol was unchanged after 5 weeks of withdrawal. Comparisons between ethanol-induced fluidization at the 1st and 5th week after withdrawal were not significantly different. These studies demonstrate differences in ethanol-induced fluidization between alcoholic patients and control subjects that are consistent with earlier ESR studies using an animal model.

Effect of chronic ethanol feeding on rat hepatocytic glutathione. Compartmentation, efflux, and response to incubation with ethanol

Hepatocytes from rats that were fed ethanol chronically for 6-8 wk were found to have a modest decrease in cytosolic GSH (24%) and a marked decrease in mitochondrial GSH (65%) as compared with pair-fed controls. Incubation of hepatocytes from ethanol-fed rats for 4 h in modified Fisher's medium revealed a greater absolute and fractional GSH efflux rate than controls with maintenance of constant cellular GSH, indicating increased net GSH synthesis. Inhibition of gamma-glutamyltransferase had no effect on these results, which indicates that no degradation of GSH had occurred during these studies. Enhanced fractional efflux was also noted in the perfused livers from ethanol-fed rats. Incubation of hepatocytes in medium containing up to 50 mM ethanol had no effect on cellular GSH, accumulation of GSH in the medium, or cell viability. Thus, chronic ethanol feeding causes a modest fall in cytosolic and a marked fall in mitochondrial GSH. Fractional GSH efflux and therefore synthesis are increased under basal conditions by chronic ethanol feeding, whereas the cellular concentration of GSH drops to a lower steady state level. Incubation of hepatocytes with ethanol indicates that it has no direct, acute effect on hepatic GSH homeostasis.

Binding of [14C] DDT by submitochondrial particles

1. Binding of [14C] DDT by submitochondrial particles and by liposomes prepared from lipids extracted from the particles was studied by the discontinuous sucrose gradient method. 2. Binding of the insecticide was a biphasic linear function of the biomembrane- and liposome-concentration with a break in the binding curve occurring at identical concentrations of phospholipid for both the biomembrane and vesicle. The biphasic binding curve is interpreted in terms of decreased availability of binding sites as a result of particle-particle interaction. 3. [14C] DDT was bound mainly by the membrane lipids and only negligible binding was detected for the delipidated membrane. 4. A 100-200-fold excess of unlabeled DDT had no effect on the binding of [14C] DDT and a 600-fold excess of unlabeled DDT reduced the binding by 20% suggesting that binding of [14C] DDT by lipids was nonspecific. 5. These results are discussed in relation to the strong inhibition by DDT of mitochondrial bioenergetics.

Effect of ethanol on amylase secretion and cellular calcium homeostasis in pancreatic acini from normal and ethanol-fed rats

The effects of ethanol on stimulus-secretion coupling were assessed by studying amylase release, Ca2+-homeostasis, and changes in physical properties of membranes in isolated rat pancreatic acini. In acini from normal rats, ethanol (50 mM and above) in vitro caused a dose-dependent stimulation of amylase release and an increase in cytosolic free Ca2+ concentration. Ethanol did not affect amylase secretion stimulated by cholecystokinin-octapeptide (CCK8), a secretagogue that acts by increasing cytosolic free Ca2+ levels, but did potentiate the secretion of amylase induced by vasoactive intestinal peptide (VIP) which raises intracellular cAMP. Ethanol also increased the rate of 45Ca2+ exchange. In acini labeled with the spin-probe 12-doxyl stearic acid, ethanol disordered the pancreatic plasma membranes. By contrast, in acini from animals that had chronically (6-7 weeks) ingested ethanol, the membranes were resistant to this disordering effect of ethanol. Chronic ethanol feeding lowered the total cellular calcium content and ionophore (A23187)-releasable pools of acinar calcium (11 and 24% respectively), and led to a 15-30% decrease in the rate of 45Ca2+ exchange. Chronic ethanol ingestion also lowered the basal rate of amylase secretion, but ethanol in vitro stimulated amylase secretion more than in control preparations. However, these differences in basal and ethanol-induced amylase secretion were not accompanied by corresponding changes in intracellular free Ca2+. The data suggest that ethanol perturbs cell membranes and also disturbs cellular Ca2+ homeostasis. These effects may explain its actions as a weak Ca2+-mediated secretagogue. However, the membrane alterations induced by chronic ethanol feeding do not prevent the ethanol-induced interference with cellular calcium homeostasis.

Abnormal membrane properties of the sarcoplasmic reticulum of pigs susceptible to malignant hyperthermia: modes of action of halothane, caffeine, dantrolene, and two other drugs

The role of sarcoplasmic reticulum (SR) in malignant hyperthermia (MH) was studied using the heavy microsomal fraction prepared from semitendinosus muscles of both normal and genetically MH-susceptible pigs. In the presence of ATP, SR was loaded with 70 nmol Ca2+/mg SR protein. Under these conditions, MH-SR demonstrated Ca2+-induced Ca2+ release (Ca-ICaR) and halothane-induced Ca2+ release (halothane-ICaR; halothane concentrations as low as 10 microM). Normal SR did not demonstrate these release phenomena. Dantrolene inhibited the halothane-ICaR, but did not inhibit the Ca-ICaR. Ruthenium red and tetracaine inhibited both types of Ca2+ release. From the measurement of passive Ca2+ efflux, it was shown that dantrolene did not affect the Ca2+ permeability of the SR itself, but suppressed only the halothane-induced increment of the permeability. The membrane order parameter of the SR, as measured by the spin-probe EPR technique, indicated that halothane disordered the lipid bilayer of MH-SR to a greater extent than it did of normal SR. This halothane disordering effect on MH-SR was antagonized by dantrolene. Ruthenium red and tetracaine did not antagonize the halothane disordering effect. These results raise the possibility that halothane could disturb the structure of the lipoprotein complex in MH-SR in such a way that it could open the Ca2+-release channels. The Ca2+ thus released further opens the channel through the Ca-ICaR mechanism in a positive feedback fashion, thus triggering the MH syndrome. The efficacy of dantrolene in ameliorating the MH syndrome might be related to the inhibition of this halothane effect.

Immunochemical evidence for an inactive form of cytochrome oxidase in mitochondrial membranes of ethanol-fed rats

Previous studies have established that rats fed ethanol chronically exhibit a 50% decrease in hepatic mitochondrial cytochrome oxidase compared to pair-fed controls, based on both heme aa3 content and specific activity. To determine whether the 'missing' 50% of cytochrome oxidase is present in the membrane but catalytically inactive, or entirely absent, we used immunochemical techniques to determine the content of cytochrome oxidase protein in hepatic submitochondrial particles. Rabbit antiserum against purified rat liver cytochrome oxidase precipitated cytochrome oxidase from detergent-solubilized submitochondrial particles. Immunoinhibition titrations of a fixed amount of anti-oxidase serum with increasing amounts of submitochondrial particle protein showed that similar percentages of added oxidase activity were recovered in supernatants after immunoprecipitation with preparations from both alcoholic and control rats. Similarly, titrations of a fixed amount of submitochondrial particle protein with increasing amounts of antiserum showed comparable decreases in oxidase activity. Equivalent amounts of protein were obtained in immunoprecipitates from both preparations. Immunoprecipitates demonstrated comparable oxidase subunit profiles by electrophoresis, except that one additional band, migrating in the region of oxidase subunit IV, was present in samples from alcoholic rats. The data indicate that cytochrome oxidase immunologic reactivity is quantitatively similar in both types of membranes. The results suggest that the 'missing' cytochrome oxidase is actually present within the membranes of alcoholic animals in an inactive form, apparently devoid of heme aa3.

The effect of temperature and chronic ethanol feeding on the proton electrochemical potential and phosphate potential in rat liver mitochondria

The relationship between the proton electrochemical potential (delta mu H) and the maximal free energy of ATP hydrolysis (delta GP) in coupled respiring rat liver mitochondria was investigated as a function of temperature and chronic ethanol-feeding. The flow dialysis method was utilized to measure the temperature dependence of delta mu H from the uptake of 86Rb (in the presence of valinomycin) and [14C]DMO. delta GP in state 4 was determined by a null-point titration of the reversible, H+-coupled ATPase against the phosphate potential. delta mu H increases with temperature from 196 mV at 10 degrees C, to 217 mV at 40 degrees C. The maximal delta GP at state 4 decreases as a function of temperature from 67.8 kJ/mol at 10 degrees C, to 54.8 kJ/mol at 40 degrees C. As a result, the ratio delta GP/delta mu H decreases with temperature from 3.56 at 10 degrees C to 2.60 at 40 degrees C. Similar studies with mitochondria from rats which were chronically fed with ethanol show that, while delta GP at state 4 decreases in these rats from 61.2 to 56.0 (25 degrees C), the delta mu H is essentially unchanged at 212 mV. Thus the ratio delta GP/delta mu H in ethanol-fed rats at 25 degrees C is 2.77 as compared with 2.97 in control. Similar reduction of delta GP was observed in inverted inner membranes from ethanol-fed rats. Both the temperature dependence of delta GP/delta mu H and the effect of ethanol-feeding cannot be easily explained by the chemiosmotic hypothesis which postulates that delta mu H is the only driving force for ATP synthesis. In contrast, a parallel coupling model, which postulates that intramembrane proton transfer from redox pumps to ATPase is mediated by the formation of dynamic aggregates of the mitochondrial inner-membrane proteins, can easily accommodate these findings. Accordingly, the temperature effect is due to weakening of these fragile aggregates, while the ethanol-feeding effect is the result of reduced concentration of active pumps, which decrease the frequency of formation of functional aggregates.

Functional properties of isolated hepatocytes from ethanol-treated rat liver

Gluconeogenesis and palmitate incorporation into triacylglycerols and phosphatidylcholine were measured in isolated hepatocytes from control and ethanol-treated rats. Basal gluconeogenesis and its hormonal response decreased in hepatocytes from ethanol-treated animals; palmitate incorporation into triacylglycerols increased. In ethanol-treated rat liver, 45Ca2+ uptake and methylating capacity were reduced, and the hormonal response exhibited differences in binding parameters of insulin.

Chronic ethanol increases liver plasma membrane fluidity

Purified plasma membrane fractions of cultured well-differentiated Reuber H35 hepatoma cells were studied after growth in the presence or absence of ethanol. Growth of cells in the presence of ethanol significantly increased plasma membrane 5'-nucleotidase activity but did not influence sodium-potassium adenosinetriphosphatase activity. Fluorescence polarization of lipophilic probes was used to study membrane lipid structure. Steady-state polarization of diphenylhexatriene (DPH), a probe of the hydrophobic core, was significantly lower in plasma membranes from cells grown in 80 mM ethanol for 3 weeks, compared to controls. Decreased polarization of DPH in plasma membranes was observed after 3-weeks growth of cells in as little as 1 mM ethanol. A 1-h exposure to 80 mM ethanol had no effect. Altered DPH polarization was due to a decrease in the order parameter of the probe. The rotational correlation time of the probe was virtually unchanged. Chronic ethanol treatment of cells did not alter the polarization of the membrane surface probe trimethylammoniodiphenylhexatriene. Plasma membranes from cells grown in 80 mM ethanol had decreased contents of both phospholipid and unesterified cholesterol, but the cholesterol to phospholipid ratio was unchanged. The percentages of sphingomyelin and phosphatidylserine in plasma membrane phospholipids were significantly decreased after ethanol treatment, while the phosphatidylcholine/sphingomyelin ratio was increased by 42%. Vesicles prepared from total plasma membrane lipids of ethanol-treated cells, as well as vesicles prepared from polar lipids alone, showed the same alterations in DPH polarization as did plasma membranes. The importance of ethanol metabolism in the observed plasma membrane changes was demonstrated in two ways.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of chronic alcohol consumption on rat brain microsome lipid composition, membrane fluidity and Na+-K+-ATPase activity

The present study reports differences in phospholipid classes, fatty acids of individual phospholipids, and changes in membrane fluidity and Na+-K+-ATPase activity in brain microsomes of rats maintained on an alcohol diet for 35 days compared to sex, age and weight-matched control rats maintained on a calorically-equivalent, non-alcohol diet. Although no difference in Na+-K+-ATPase activity was found in microsomes from alcohol vs control rats when measured in the absence of added alcohol, the presence of low concentrations of ethanol (less than 100 mM) stimulated, while high concentrations (greater than 100 mM) inhibited enzyme activity. The stimulation was differentially expressed in that the microsomal enzyme from alcohol rats was stimulated to a lesser extent than the enzyme from control rats. However, the inhibiting effect of high concentrations of alcohol was similar in microsomes from both alcohol and control rats. Also in membranes from alcohol rats, there was a lower quantity of phosphatidylethanolamine (PE) and higher quantities of phosphatidylserine (PS) and phosphatidylinositol (PI) compared to membranes from control rats. The major change in fatty acid composition was a reduction in the level of polyunsaturated fatty acids, which was particularly evident in PI and PS. The linoleic acid: arachidonic acid ratio (18:2/20:4) and the saturation:unsaturation ratio were also increased in PI and PS in membranes from alcohol animals. However, the ratio of n-6/n-3 fatty acids remained the same or was reduced in membranes from alcoholic animals. Although no difference in the inherent "fluidity" of membranes from alcohol vs control rats could be demonstrated by electron paramagnetic resonance, molecular tolerance to ethanol was demonstrated in the membranes from alcohol rats by the resistance to the disordering effects of added ethanol.

Ethanol and membrane lipids

Although ethanol is known to exert its primary mode of action on the central nervous system, the exact molecular interaction underlying the behavioral and physiological manifestations of alcohol intoxication has not been elucidated. Chronic ethanol administration results in changes in organ functions. These changes are reflective of the adaptive mechanisms in response to the acute effects of ethanol. Biophysical studies have shown that ethanol in vitro disorders the membrane and perturbs the fine structural arrangement of the membrane lipids. In the chronic state, these membranes develop resistance to the disordering effects. Tolerance development is also accompanied by biochemical changes. Although ethanol-induced changes in membrane lipids have been implicated in both biophysical and biochemical studies, measurements of membrane lipids, such as cholesterol content, fatty acid unsaturation, phospholipid distribution, and ganglioside profiles, have not produced conclusive evidence that any of these parameters are directly involved in the action of ethanol. On the other hand, there is increasing evidence indicating that although ethanol in vitro produces a membrane-fluidizing effect, the chronic response to this effect is not to change the membrane bulk lipid composition. Instead, changes in membrane lipids may pertain to small metabolically active pools located in certain subcellular fractions. Most likely, these lipids are involved in important membrane functions. For example, the increase in PS in brain plasma membranes may provide an explanation for the adaptive increase in synaptic membrane ion transport activity, especially (Na,K)-ATPase. There is also evidence that the lipid pool involved in the deacylation-reacylation mechanism (i.e., PI and PC with 20:4 groups) is altered after ethanol administration. An increase in metabolic turnover of these phospholipid pools may have important implications for the membrane functional changes. Obviously, there are other lipid-metabolizing enzyme systems that may exert similar effects but have not yet been investigated in detail. From the results of these studies, it is concluded that the multiple actions of ethanol are associated with changes in enzymic systems important in the functional expression of the membranes.

Membrane regulation of liver and lung microsomes under low oxygen tension

A highly monitorized animal model has been developed for the study of the influence of low oxygen tension on lipid composition, microviscosity and regulation of enzyme activities involved in the phospholipid synthesis of hepatic and pulmonary microsomes. Microviscosity decreased in liver microsomes whereas no difference was shown in that of microsomal membrane core of hypoxemic lung. Nevertheless, phospholipid and cholesterol content of both liver and lung membranes changed significantly. Microsomal membranes of hypoxemic liver increased the unsaturation degree of fatty acids, whereas hypoxemic lung membranes become more saturated, mainly due to the increase of palmitic acid. The adaptive response of lung was confirmed by the high increase of the deacylation-reacylation mechanism.

Chronic alcohol ingestion alters the calcium permeability of sarcoplasmic reticulum of rat skeletal muscle

Heavy sarcoplasmic reticulum (SR) was prepared from skeletal muscle of control and chronic alcoholic rats, and the effect of in vitro addition of ethanol on the passive Ca2+ permeability was studied. The SR was loaded with Ca2+ in the absence of ATP. Then efflux was initiated by adding an EGTA solution to decrease the extravesicular Ca2+ concentration. The decrease of Ca2+ content of the SR was measured by an optical method using an encapsulated metallochromic indicator (calcein). The Ca2+ permeability of alcoholic rat SR was higher than that of control rats, especially at low external Ca2+ concentrations (below 1 microM). An in vitro (acute) exposure of SR to ethanol increased the Ca2+ permeability of the SR. However, the degree of increase in alcoholic rat SR was smaller than that in control rat SR.

Sarcoplasmic reticulum membrane of rat skeletal muscle is disordered with chronic alcohol ingestion

Heavy sarcoplasmic reticulum (SR) was prepared from skeletal muscle of chronic alcoholic rats and control rats. Compared with control rat SR, the SR prepared from alcoholic rats is leakier to Ca2+ and has a lower level of maximum storable Ca2+. With in vitro exposure to ethanol, the Ca2+ release of alcoholic rat SR was not enhanced as much as that of SR prepared from control rats. By using the spin-probes 5-, 7-, 12-, and 16-doxylstearic acid, the disordering effect of ethanol on the SR membrane was studied. The results suggest that SR membrane of chronic alcoholic rats is less ordered than that of control rats even in the absence of in vitro ethanol. However, chronic SR membrane shows a greater resistance to the disordering effect of in vitro addition of ethanol than control rat SR.

The fluidity of plasma membranes from ethanol-treated rat liver

Male Wistar rats were maintained for 35-40 days on a liquid diet containing 36% of calories as ethanol. Ethanol was replaced by carbohydrates in the isocaloric diet fed to control animals. The effect of ethanol consumption has been studied on the fluorescence polarization of rat liver plasma membranes and artificial lipid vesicles and on the lipid composition of the membranes. Fluorescence polarization in both membranes and vesicles was determined using DPH and TMA-DPH as fluorescence markers; from these data, the polarization term (ro/r-l)-1 and flow activation energy (delta E) were calculated. The ethanol consumption induces a more fluid environment within the membrane core of liver plasma membranes; the ethanol-fed rat membranes are more resistant to the in vitro effect of ethanol disordering the membrane structure. Vesicles obtained with lipids from either control membranes or ethanol-fed rat membranes were treated with ethanol and the changes in polarization paralleled to those exhibited by the membranes. The absence of phase transitions and of delta E changes was also shown in temperature-dependence studies. The lower cholesterol content found in ethanol-fed rat plasma membranes might be responsible for observed variations in the microviscosity.

Biochemical and morphological alterations of baboon hepatic mitochondria after chronic ethanol consumption

Baboons fed ethanol (50% of total calories) chronically develop ultrastructural alterations of hepatic mitochondria. To determine whether mitochondrial functions are also altered, mitochondria were isolated from nine baboons fed ethanol chronically and their pair-fed controls. At the fatty liver stage, ADP-stimulated respiration was depressed in ethanol-fed baboons by 59.4% with glutamate, 43.2% with acetaldehyde, 45.1% with succinate and 51.1% with ascorbate as substrates. A similar decrease was noted in the ADP/O ratio (14 to 28%) and respiratory control ratio (20 to 44%) with all substrates. Similar alterations of mitochondrial functions were observed in baboons with more advanced stages of liver disease, namely fibrosis. These changes after ethanol treatment were associated with decreases in the enzyme activities of mitochondrial respiratory chain: glutamate, NADH and succinate dehydrogenase (42, 24 and 28%, respectively), glutamate-, NADH- or succinate-cytochrome c reductase (42, 27 and 32%, respectively) and cytochrome oxidase (59.6%). The content of all cytochromes was also decreased in ethanol-fed baboons, especially aa3 (57%). Moreover, [14C]leucine incorporation into mitochondrial membranes was depressed by 21% after ethanol treatment. On the other hand, glutamate dehydrogenase activities of serum and cytosol in ethanol-fed baboons were significantly higher than those in pair-fed controls. Morphologically, mitochondria of ethanol-fed baboons were larger than those of pair-fed controls. However, the mitochondrial protein content per mitochondrial DNA was unchanged. From these results, we conclude that, morphologically and functionally, hepatic mitochondria in baboons are altered by chronic ethanol consumption; it is noteworthy that these changes are fully developed already at the fatty liver stage, and that morphological alteration appears to reflect the damage of mitochondrial membranes rather than an adaptive hypertrophy.

Membrane potential and surface potential in mitochondria. Binding of a cationic spin probe

The interaction of the cationic spin probe 4-(N,N-dimethyl-N-dodecyl)-ammonium-2,2,6,6-tetramethyl-piperidine-1-oxyl (Cat12) with intact mitochondria and submitochondrial particles was investigated as a function of salt concentration, pH and energization by ATP. In the presence of 1 mM Fe(CN)-36, which inhibits the probe reduction by the mitochondria, the probe signal is stable and shows both bound and free forms. The partition of the probe into mitochondrial membranes is decreased by various salts depending on the cation valency, indicating that the membrane is negatively charged (-10 to -15 mV at pH 7.0). The surface potential increases with pH from -3 mV at pH 5.0 to -18 mV at pH 8.0. Energization of intact mitochondria by ATP reduces the magnitude of both bound and free signals by more than 50%; the signal of the bound form slowly disappears on further incubation. The ATP effect is inhibited and also reversed by either oligomycin or CCCP. Similar effects of ATP were observed in mitoplasts but not in submitochondrial particles. In submitochondrial particles ATP has no effect on the probe signal or binding. These results suggest that the formation of membrane potential in mitochondria induces uptake and internal binding of the probe which results in broadening of the EPR signal of the internally bound probe. It is concluded that Cat12 is not a suitable probe for measurement of surface potential in energized mitochondria.

Alcohol and the heart

Acute alcohol ingestion can lead to alterations of either mechanical function or electrophysiologic properties of the heart, whereas chronic consumption can lead to progressive cardiac dysfunction and congestive cardiomyopathy. On the other hand, alcohol appears to have a protective effect for coronary artery disease when consumed in low amounts, although prophylactic use of alcohol is not recommended.

Effects of Cd2+ on ATP-driven membrane potential in beef heart mitochondrial H+-ATPase: a study using the voltage-sensitive probe oxonol VI

Beef heart mitochondrial H+-ATPase (F1-F0) vesicles were prepared by lysolecithin extraction of ETPH. ATP-driven membrane potential was monitored indirectly by following absorbance changes of the potential-sensitive dye oxonol VI. The steady-state potential was discharged by oligomycin and/or Cd2+ (a dithiol reagent). At 13 degrees C, the agents appeared to act synergistically; at 24 degrees C the data were equivocal. When Cd2+ was added before energization, the membrane potential was markedly attenuated. Both effects of Cd2+ were inhibited by dithiothreitol. The activation energy for oligomycin-sensitive ATPase exhibited a discontinuity at 16 degrees C. However, the temperature dependence of the rate of potential discharge by oligomycin showed no such discontinuity. The results are discussed in terms of the involvement of thiol groups in proton translocation and the thermotropic behavior of the membrane vesicles.

Differential effect of lipid peroxidation on membrane fluidity as determined by electron spin resonance probes

The effect of lipid peroxidation on membrane fluidity was examined in sonicated soybean phospholipid vesicles. Following iron/ascorbate dependent peroxidation, the vesicles were labeled with a series of doxyl stearate spin probes which differed in the site of attachment of the nitroxide free radical to the fatty acid. Comparison of motional and partitioning parameters derived from electron spin resonance spectra of the probes indicated that the membranes were less fluid following peroxidation. However, the magnitude of the fluidity decrease was markedly dependent on the intramembrane location, as well as on the extent of lipid peroxidation. The effect of lipid peroxidation on fluidity was maximal in the membrane microenvironment sampled by 12-doxyl stearate, whereas other regions of the bilayer were less affected. These findings indicate that lipid peroxidation leads to an alteration of the transbilayer fluidity gradient.

Uncoupling of oxidative phosphorylation in rat liver mitochondria by general anesthetics

The general anesthetics chloroform and halothane inhibit ATP synthesis in rat liver mitochondria, in the millimolar concentration range (1-12 mM), in parallel with a reduction of respiratory control and the ratio of ATP produced to oxygen consumed. In these effects, halothane and chloroform are similar to classical, protonophoric, uncouplers. The rate of ADP-stimulated respiration or the rate of uncoupler-stimulated respiration is not affected. Like classical uncouplers, halothane and chloroform also stimulate mitochondrial ATPase activity. However, the extent of stimulation by these agents is larger than by protonophoric uncouplers and, more significantly, ATPase activity stimulated by carbonylcyanide m-chlorophenylhydrazone is further stimulated by these agents. In the presence of the Ca2+ chelator EGTA, halothane and chloroform have no measurable effect on the magnitude of the proton electrochemical potential, delta mu H. In the absence of EGTA these anesthetics have a small effect on delta mu H, apparently due to stimulation of Ca2+ cycling. Under these conditions the membrane potential is decreased while delta pH is increased, but the total value of delta mu H is only slightly decreased. The uncoupling activity of the anesthetics is the same in the presence of absence of EGTA. Thus, in contrast to protonophoric uncouplers, the uncoupling effect of general anesthetics does not depend on the collapse of delta mu H. In the same concentration range in which anesthetics uncouple oxidative phosphorylation both halothane and chloroform increase membrane fluidity, as measured by the partitioning of the hydrophobic spin probe 5-doxyldecane. These findings suggest a role for intramembrane processes in energy conversion that is not dependent on the bulk delta mu H.

Ethanol and biological membranes: injury and adaptation

Ethanol intoxication affects the protein and lipid constituents of biological membranes. Mitochondria exhibit specific decreases in components of the electron transport chain and in protein synthesis. In vitro ethanol reduces the transition temperatures of membrane-bound enzyme activities and decreases the order parameter. On the other hand, both are increased after chronic ethanol administration. After chronic ethanol treatment membranes are resistant to disordering by ethanol, possibly owing to an increased saturation of mitochondrial phospholipids, particularly cardiolipin. The increased rigidity of mitochondrial and synaptosomal membranes is associated with reduced binding of ethanol and of the general anesthetic halothane. The data suggest that initially ethanol increases the fluidity of all biological membranes. If continued chronically, this effect is balanced by a change in the lipid composition of the membranes, which increases their rigidity and makes them resistant to disordering by ethanol (homeoviscous adaptation). The change in molecular order reduces the binding of ethanol and other compounds, but also impairs a variety of membrane-bound functions. These changes may play a role in tolerance to ethanol and cross-tolerance to anesthetics, and in the pathogenesis of maladies associated with alcohol abuse.